Conventionally, Japanese Published Unexamined Patent Application No. 180422/1984 (travel locus analyzing system) is named as disclosing a system which measures and utilizes the 3-dimensional position of a vehicle in order to support the driving of a work vehicle and automate the work in a building site.
This system samples the travel speed, longitudinal tilt angle, lateral tilt angle and azimuth of the moving vehicle at fixed infervals and calculates the current position of the vehicle on the basis of the sampled values at fixed intervals.
This conventional system accumulates the quantities of relative movement of the vehicle and calculates the current position of the vehicle, so that it has the problem that an accumulated error may be involved in the current position of the vehicle due to the roughness of the road, the wheel slippage or errors in the sampled values to thereby lower the accuracy with which the position of the vehicle is measured.
Systems are proposed which measure the position of a moving body in accordance with the principles of triangulation by scanning the work area with laser beams from two rotary laser projectors installed in the work area in order to measure the 3-dimensional position of a vehicle.
One of the systems is disclosed, for example, in Japanese Published Examined Patent Application No. 1521/1977, in which the difference between the time when the laser beam from each of two rotary laser projectors crosses the reference azimuth connecting the two projectors and the time when the laser beam from that projector crosses the azimuth of the moving body are measured, the angle between both the azimuths are calculated and the principles of triangulation is applied.
This system uses a common reference azimuth signal on the assumption that the rotations of the two projectors are synchronized with high accuracy. Actually, it has the difficulty that it cannot avoid the generation of an error in the rotational synchronism of the two projectors due to unequal characteristics of the rotational drivers of the projectors and a change of the environment, so that the accuracy with which the position of the moving body is measured is greatly degraded.
In utilizing the measured data, a method is often employed which displays the current position of a moving body on a map and controls the vehicle travel on the basis of this display.
Conventionally, almost all of the position display means used for control in a travel control system for a moving body, such as a vehicle, includes a map sheet including a transparent sheet with a map printed thereon, attached on a display screen or a projector or the like to display a microfilm map, to thereby display terrain information thereon and plot (or trace) the position information obtained from a gyro sensor, loran or the like on the terrain information.
It is assumed in such position display means that a terrain does not change at all, so that the position display means has the problem that it cannot be used at all for an hourly changing terrain such as a construction site where the ground is being levelled.
The present invention has been made in view of the above real situation. It is an object of the present invention to provide a position measuring apparatus which is capable of measuring with high accuracy the 3-dimensional position and attitude angle of a moving body, such as a vehicle, on a real-time basis, even in a construction site where the shape of the work area surface changes very often.